There are several types of pain, including neuropathic pain (such as sciatica—see see What Is Sciatica?), nociceptive pain (such as pain after surgery and pain due to cancer), and psychogenic pain.
Neuropathic pain is caused by damage to or dysfunction of the nerves, spinal cord, or brain.
Neuropathic pain may be felt as burning or tingling or as hypersensitivity to touch or cold. Causes include compression of a nerve (for example, by a tumor, by a ruptured intervertebral disk, or as occurs in carpal tunnel syndrome), nerve damage (for example, as occurs in a metabolic disorder such as diabetes mellitus), and abnormal or disrupted processing of pain signals by the brain and spinal cord. Processing of pain is abnormal in phantom limb pain, postherpetic neuralgia, and complex regional pain syndrome.
Phantom Limb Pain:
Pain seems to be felt in an amputated part of the body, usually a limb. It differs from phantom limb sensation—the feeling that the amputated part is still there—which is much more common. Phantom limb pain cannot be caused by a problem in the limb. Rather, it must be caused by a change in the nervous system above the site where the limb was amputated. But the brain misinterprets the nerve signals as coming from the amputated limb. Usually, the pain seems to be in the toes, ankle, and foot of an amputated leg or in the fingers and hand of an amputated arm. The pain may resemble squeezing, burning, or crushing sensations, but it often differs from any sensation previously experienced. For some people, phantom limb pain occurs less frequently as time passes, but for others, it persists. Massage can sometimes help, but drug therapy is sometimes necessary.
This disorder results from herpes zoster (shingles, which causes inflammation of nerve tissue), but occurs only after shingles resolves (see see Sidebar 2: What Is Postherpetic Neuralgia?). What causes postherpetic neuralgia is unknown. The pain is felt as a constant deep aching or burning, as a sharp and intermittent pain, or as hypersensitivity to touch or cold. The pain may be debilitating. Pain relievers and other drugs may be required, but no treatment is routinely effective.
Complex Regional Pain Syndrome:
This chronic pain syndrome is defined as persistent burning pain accompanied by certain abnormalities that occur in the same area as the pain. Abnormalities include increased or decreased sweating, swelling, changes in skin color, damage to the skin, hair loss, cracked or thickened nails, muscle wasting and weakness, and bone loss. This syndrome typically occurs after an injury. There are two types:
Sometimes complex regional pain syndrome is made worse by activity of the sympathetic nervous system, which normally prepares the body for stressful or emergency situations—for fight or flight. For this reason, doctors may suggest treatment with a sympathetic nerve block (see see Anesthetics). Physical therapy and drugs may also help.
Nociceptive pain is caused by an injury to body tissues.
The injury may be a cut, bruise, bone fracture, crush injury, burn, or anything that damages tissues. This type of pain is typically aching, sharp, or throbbing. Most pain is nociceptive pain. Pain receptors for tissue injury (nociceptors) are located mostly in the skin or in internal organs.
The pain almost universally experienced after surgery is nociceptive pain. The pain may be constant or intermittent, often worsening when a person moves, coughs, laughs, or breathes deeply or when the dressings over the surgical wound are changed.
Most of the pain due to cancer is nociceptive. When a tumor invades bones and organs, it may cause mild discomfort or severe, unrelenting pain. Some cancer treatments, such as surgery and radiation therapy, can also cause nociceptive pain. Pain relievers (analgesics), including opioids, are usually effective.
Psychogenic pain is pain that is mostly related to psychologic factors.
When people have persistent pain with evidence of psychologic disturbances and without evidence of a disorder that could account for the pain or its severity, the pain may be described as psychogenic. However, psychophysiologic pain is a more accurate term because the pain results from interaction of physical and psychologic factors. Psychogenic pain is far less common than nociceptive or neuropathic pain.
Any kind of pain can be complicated by psychologic factors. Psychologic factors often contribute to chronic pain and may contribute to pain-related disability. In such cases, the pain, disability, or both usually have a physical cause, but psychologic factors exaggerate or enhance the pain, making it worse than what most people with a similar physical disorder experience. For example, people with chronic pain know it will recur and may become fearful and anxious as they anticipate the pain. These emotions make them more sensitive to pain. Sometimes doctors describe chronic pain that is worsened by psychologic factors as a chronic pain syndrome.
The fact that pain is caused or worsened by psychologic factors does not mean that it is not real. Most people who report pain are really experiencing it, even if a physical cause cannot be identified. Doctors always investigate whether a physical disorder is contributing to pain.
Pain complicated by psychologic factors requires treatment, often by a team that includes a psychologist or psychiatrist. Treatment for this type of pain varies from person to person, and doctors try to match the treatment with the person's needs. For most people who have chronic psychogenic pain, the goals of treatment are to improve comfort and physical and psychologic function. Doctors may make specific recommendations for gradually increasing physical and social activities. Drugs and nondrug treatments—such as biofeedback, relaxation training, distraction techniques, hypnosis, transcutaneous electrical nerve stimulation (TENS), and physical therapy—may be used. Psychologic counseling is often needed.
Last full review/revision August 2007 by Russell K. Portenoy, MD